1. Field of the Invention
The present invention generally relates to a signal processing circuit for slicing binary signals in a receiver. More particularly, the present invention relates to a signal processing circuit that generates an adaptive slicer threshold by using either average amplitude data of both binary ones and binary zeros, or minimum amplitude data of a binary one and maximum amplitude data of a binary zero.
2. Discussion of the Related Art
Data communication using binary signals takes place at high rates in various applications. For example, in optical data systems, data transmission rates of 10 gigabits/second (Gb/s) and higher are utilized. In such binary data communication systems, a receiver is used for receiving the binary signals from a transmitter. In many cases, the signals received are of a low level and are accompanied by noise and/or jitter (see FIG. 2). The true binary nature of a distinct rectangular pulse, usually designating a binary one, sometimes can be partly obscured by noise, and result in data errors that adversely affect signal processing equipment to which the output of the receiver is applied.
To improve the ability to accurately recapture the binary signals passing through the receiver before being supplied to other equipment, a slicing technique is employed. This technique involves slicing the received binary signal at a level about the midpoint of its amplitude, that is, between its maximum and minimum values. The portion of the received binary signal appearing above the slicing level corresponds to a binary one and the portion below the slicing level corresponds to a binary zero (see FIG. 1 and FIG. 2).
In one type of prior art slicer circuit, the slicer threshold is fixed at a certain voltage level. A variable offset voltage is combined with the voltage level of the received binary signal to maintain the midpoint of the binary signal that is applied to the slicer at the fixed slicer threshold. However, adjusting the received binary signal to maintain the midpoint of the binary signal at a fixed level adds complexity to a system.
In another type of prior art slicer circuit, the slicer threshold is varied so as to be at the midpoint of the amplitude of the binary signal, wherein the midpoint is calculated to be the average of the maximum and minimum values of the received binary signal. However, the midpoint that is calculated using the maximum and minimum values of the received binary signal is the midpoint between the outer edges of the data eye 100, 200 (see FIG. 1 and FIG. 2). The data eye 100, 200 is a plot of sampled data values for a given time period. This method is incapable of accurately determining the midpoint between either the average values of the data eye 100, 200 edges or the inner edges of the data eye 100, 200.
Thus, a slicer circuit that is capable of accurately determining the midpoint between the average values of the data eye 100, 200 or the inner edges of the data eye 100, 200 is required.